A stint would be a short period of time. It's not used very often in the US, but when it is used, it seems to devalue the amount of time discussed. Like if someone said that he had " a stint in jail" they would be just mentioning the short time in jail, but probably continuing the sentence with what happened after the fact. For example, "After a stint in jail, he cleaned up, got a job, and started a family."  I've usually heard it used in combination with the word short - "a short stint". 

It's just a word for a period of unspecified length, like "spell".  Though the time is unspecified, the sense it is that it is long enough to be significant in your life or career. 

Good explanation Jessica. Thanks

Sir Please give an example